[linux-lvm] Fun and games with mirroring

[Les Mikesell]

On Wed, May 23, 2012 at 1:32 PM, Stuart D Gathman <stuart at bmsi.com> wrote:
> >
>> The unfortunate part is that most linux distributions don't allow
>> installation on a 'broken mirror' or have a way to convert from
>> non-raid to raid after the install the way you can on a windows server
>> - or if there is, I haven't found it.  So even if you like the new
>> replacement that you tried on the single-disk install, you have to
>> throw it away and re-install on raid in the end.
>
>
> I do this all the time - but with MD raid.  Use custom install, and
> create RAID1 MD devices in the install with only 1 leg.  You can add
> mirrors later with mdadm.

I've done that manually in a separate virtual terminal during the
install, partly because the installer likes to re-arrange the order of
the partitions on the disk when you define them there and partly
because it didn't occur to me that the installer would accept a raid1
with only one member.  Maybe I'll give it another try.  But with the
installer willing to align things on 2M boundaries these days you'd
think there would be a way to set things up so you could back in
whatever MD needs later.

> My only complaint with the MD driver is that it doesn't divide up drives
> into small partitions.  I often end up creating 2 or 3 partitions on a
> drive,
> and mirroring each.

I thought these days you could raid the whole disk and put partitions
on the raid, although I've never done it that way.  I have 2
complaints about MD.  One is that it doesn't handle errors/retries on
members very well - it will kick members that are perfectly fine
running standalone or as the last remaining member, and the other is
that partitions over 2TB need a new format that the kernel doesn't
auto-detect.  Much of the reason I liked MD in the first place was its
ability to assemble things correctly at boot regardless of the drive's
physical attachment or location.

-- 
  Les Mikesell
    lesmikesell at gmail.com